Conventionally, in an image forming apparatus such as an MFP and the like, a toner image on a photoconductive drum is transferred to a transfer belt. The toner image transferred to the transfer belt is then transferred to an image receiving medium (paper) by a transfer roller. The transfer belt is rotated through the rotation of a driving roller. The driving roller is arranged opposite to the transfer roller.
When the sheet passes through the space between the driving roller and the transfer roller, transfer voltage is applied to the sheet so that the toner image on the transfer belt can be transferred to the paper.
A conduction path is arranged in the transfer roller to apply the transfer voltage (also referred to as bias). The conduction path may include a leaf spring in contact with a metal shaft of the transfer roller. Alternatively, there is an example in which a leaf spring is in contact with a conduction section assembled to the metal shaft. The leaf spring is electrically connected to a high-voltage path or to ground.
When arranging the transfer roller on a sheet conveyance path, it is necessary to make the jam processing (sheet jam releasing) easier. Thus, a transfer unit including the transfer roller is arranged in such a manner that the transfer unit can be opened and separated from the main body of the image forming apparatus. Consequently, the conduction path of the transfer roller is arranged at the side of the opened part. The conduction path at the side of the opened part is electrically connected to the main body, and so it is necessary to arrange the conduction path near the fulcrum of the opened part.
However, conduction paths of other electrical components are also arranged near the fulcrum, and so lots of conduction paths crowd the fulcrum region. As a result, the space needed to guarantee the creepage distance is increased for the paths needed to apply the transfer bias. Further, when the leaf spring is grounded, it is necessary to arrange a ground line, which leads to an increase in the number of the electrical components.